1. Field of the Invention
The present invention relates to an auto bumper and its manufacturing process.
2. Description of the Prior Art
An auto bumper is a piece attached to the front and rear of a car to serve as a cushion in a collision, thereby protecting the auto body and the driver. Particularly in the case of a passenger car, the aesthetic requirement of the bumper, which appears on the outside of the vehicle, is stressed in addition to the above requirement.
The conventional auto bumpers can be broadly classified into:
1. Energy absorbing types such as the stable type consisting of (a) a steel bumper plus a shock absorber (Menasco type) or (b) a polyurethane bumper, and the non-stable type consisting of a bumper made of fiber reinforced plastics (FRP) which can absorb the energy of destruction itself.
2. Ordinary types such as a steel bumper alone.
The last-mentioned steel bumper, which has been popularly used, has drawbacks in that it is heavy, thereby increasing the vehicle inertia. Moreover, since it is fitted at the front and rear ends of a vehicle, it is unfavorable for controlling longitudinal vibrations of the vehicle, i.e., so-called pitching. By contrast, the polyurethane bumper is light and can restore itself after a collision, but it cannot be given a metallic lustre and it is thus limited in design versatility. Meanwhile the FRP bumper, which is usually metallic-coated or metallized for aesthetic reasons, defies a treatment to give it a durable metallic lustre. On the other hand, the conventional composite bumper of stainless steel and FRP lacks adequate adhesion of the two elements at the interface thereof.
It is not always necessary that stainless steel and FRP be bonded with each other from a functional point of view, but a good adhesion between the two elements provides a pleasant feel of structural integrity, thereby enhancing the commercial value of the bumper and contributing to its rigidity as well as reducing its weight. Thus, good adhesion has been one of the important requirements in a bumper of this kind.